Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor having one or more rotor blades. The rotor blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through the gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Such configurations may also include power converters that are used to convert a frequency of generated electric power to a frequency substantially similar to a utility grid frequency.
Renewable energy power systems, such as the wind turbine described above, typically includes a power converter with a regulated DC link controlled by a converter controller. More specifically, wind driven doubly-fed induction generator (DFIG) systems or full power conversion systems, typically include a power converter with an AC-DC-AC topology. For many wind turbines, the operating space, and hence value to the customer, is limited by maximum voltages for one or more wind turbine components inherent to DFIG systems. For example, under some operating conditions, the wind turbine may be required to provide reactive power to the power grid, which may impose over-voltage conditions on secondary transformer windings where the power converter is connected. Thus, when the power converter provides reactive power, the resulting voltage may exceed a maximum specified continuous operating voltage level.
In order to mitigate such over-voltage conditions, the converter controller can shift the power factor away from the customer demanded set points; however, this is not always optimal. Further, such limitations tend to be more significant for DFIG generators that operate at a high rated slip (RPM) or for generators that are experiencing an over-speed condition.
Thus, the art is continuously seeking new and improved system and methods for optimizing wind turbine operation for the customer while also maintaining voltage levels within specified operating limits. Accordingly, the present disclosure is directed to a system and method for optimizing wind turbine operation using a tap changer that allows the power grid to extract all available reactive power from the power converter without creating over-voltage conditions.